. Biology. Biology. NERVOUS SYSTEM OF THE LOBSTER 179 nal segments are straightened out. These flexor and extensor muscles thus act quite differently from the dermal musculature of the earthworm. Other important muscles work the various ap- pendages, of which those of the giant chelae are the most highly developed. Still others manipulate the gastric mill, theeyes, etc. THE NERVOUS SYSTEM.—In general arrangement, the nervous system of the lobster is strik- ingly similar to that of the worm; here again we find a ventral chain of nerve gan- glia which, however, are dor- sal to the ventral blood
. Biology. Biology. NERVOUS SYSTEM OF THE LOBSTER 179 nal segments are straightened out. These flexor and extensor muscles thus act quite differently from the dermal musculature of the earthworm. Other important muscles work the various ap- pendages, of which those of the giant chelae are the most highly developed. Still others manipulate the gastric mill, theeyes, etc. THE NERVOUS SYSTEM.—In general arrangement, the nervous system of the lobster is strik- ingly similar to that of the worm; here again we find a ventral chain of nerve gan- glia which, however, are dor- sal to the ventral blood vessel. A pair of cerebral ganglia, close to the eyes, innervates these and adjacent organs. A long pair of circumoe- sophageal commissures con- nects the cerebral with the first ventral or sub-cesoph- ageal ganglia. These, how- ever, represent a fusion of thoracic ganglia, for just as the somites here have merged to form the cephalo- thorax, so these ganglia have fused into one. Between the fourth and fifth ganglia,. otocyst of the lobster the double nerve COrd splits opened, showing sensory hairs and otoliths. ,1,1 i (From Gerstaecker after Farre.) and allows the sternal artery to pass through. In the abdomen, the nerve chain is quite regular and similar to that of the earthworm, in having one pair of ganglia to each somite (Fig. 73). SENSE ORGANS. — In the earthworm, we have seen that there is a well-marked advance in nerve-organization over forms like Hydra, with grounds for dividing it into peripheral sensory and internal central nervous systems. The peripheral system con- sists of more or less isolated sensory cells with their nerve. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Calkins, Gary N. (Gary Nathan), b. 1869. New York, H. Holt and company
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